Preparation of aromatic hydrocarbons from hydrocarbon mixtures



Dec. 17, 194,6.

E. A. NARAGoN PREPARATION OF AROMTIC HYDROCARBONS FROM HYDROCARBONMIXTURES Filed July 4,

III

.Juru Ill ,IIIIII Hls ATT RNEY Patented Dec. 17, 1946 PREPARATION: F..ARoMrro: HYDRO- oARBoNs FRoM HYDRoCARBoN M1X- TURES Ernest A. Naragon,Se-a-con, Y.,assignor to The Texas CompanyyNew York, N. Y., acorporation or `llelavvare i Application July 2i, 1944,;seia1N. straits5 Claims.

(C1. 19e-isf o This invention relates to the preparation ofr` aromatichydrocarbons from hydrocarbon. mixtures and particularly from naphthahydrocarbon mixtures.

The invention contemplates processior ex- Cil tracting aromatichydrocarbons fromfeed hydrot carbon .mixtures of aromatics andnon-aromatics which comprises subjectingfa feed hydrocarbon mixtureV tocontact with anfaluminum halide-hydrocarbon .complex of theFriedel-Crafts type.4

The contact is. carried out under conditions so as to forma primaryextract-phase comprising oom-` .u plex aromatic'hydrocarbons and 4some4nor'i-varow- .u matic` hydrocarbons .and a primary vraiiinataV phaseconsisting essentially of non-aromatic hydrocarbons such as paraffinsand naphthenes.` The raffinate phase is discharged and the extractAphase subjected to contact with a `Wash solvent under conditions solas`to displace non-aromatic 1 hydrocarbons retained `in vthe primaryextract i phase, leaving asecondary extract phase. This1A secondaryextract phase, consisting essentially` of complex, aromatichydrocarbons, and a small amount of wash solvent is .then subjected to-cony tact with a further quantity of wash solventsoas to displace fromthe complex aromatic hydrocarbons which after separation from the Washsolvent lwill be in a highly concentrated form.

The process is particularly applicable to the separation of aromaticsfrom naphtha feed hydrocarbon mixtures.. containing aromatics amountingto from 10 to .80% `by volume of the feed mixture using an aluminumchloride-hydrocarbon complex characterized by .having a heat u ofhydrolysis of about 290 to 330 small calories per gram of complex.

The complex maybedthat obtained by reacting aluminum chloride withkerosene in the presence of hydrogen chloride yat a temperature of`about 200to 250 F. However, thecomplex may comprise that which is formedin situ during the operation of the process as a result of reactionbeytween free aluminum halide anda small propor-V tion of the aromaticconstituents of the hydrocarbons undergoing treatment.

n feature of the process has` to do `Witlothe sep- Y,

aration of aromatic hydrocarbons from.non-aro-A matic hydrocarbons whichare coextensive in boilu ing range,v Aluminum halide-hydrocarbon{com-.

plexes exert a high degree of solvent action upon aromatic hydrocarbonsandthis .solvent action mayinvolve somecombination betweenthe aluminumhalide andaromatic hydrocarbons. However.. nQn-aromatia .hydrocarbons.also renato.

form combinations with aluminum halide, These latter` combinations areapparently of more loose character than the aromatic complexcombinations, f. f u l Ifhav@ found that when extracting aromatic`hydrocarbonsl from naphtha mixtures with analuminum(chloride-hydrocarbon complex the resulting .extract phasecomprises complex and aromatichydrocarbons` and theresulting mixture is.alsorvmore-or .less saturated withV paran and naphthenehydrocarbons..It has been found that the parain and .naphthene hydrocarbons retainedinlthe extract phase can be displaced therefrom .by washing the. extractphase with a saturated hydrocarbonwofl diierent boilingl range;thatisboiling outside the range of the aforesaid retained hydrocarbons.l .I

ihewashing treatment .can becarried out under conditions such that theretained non-aro-l matic4 .hydrocarbons ,are displaced `without sub-vstantial displacement. ofthe aromatic `constituents., Also.V thewashedextractphase from which the .retained paramns .and naphthenes havebeen displacedcan then be subjectedto further Washv ing, using a largersolvent dosage so as to displace aromatic ylfiydrocarbons from thecomplex. The

complex now strippedof aromatic hydrocarbons.

canthentbe, recycled. for the extraction of fresh feed hydrocarbonmixtures.

Thus, in `accordance .with the'v invention, a primary `extract phasecomprising complex, aromatic hydrocarbons and some non-aromatichydrocarbonshcoextensive in boiling range iswashed with a saturatedpetroleum. hydrocarbon boiling` infthe range eithersubstantiallybeloworsubstantially. abovey that ofthe extract hydrocarbons. Thelwashingiseffected in two stages.. In the iirst washingistage, VarelativelyloWlsolyent dosage is employed so astodsplacethe non-aromatic ex- `tracthydrocarbons, while` inthe second stage a relativelymhignsolventdosageis employed so as to j -displace thearomatia extract .hydrocarbons'rom the; complex., The ,displaced hydrocarbons removed from eachwashing stage are subsequently fractionated from the washsolvent liquidwith which they maybe associated. A

ReferenceA will now be made to the` accompanying drawing showingadiagramof flow useful in carrying qutthe process.

Referring to the drawing, a feed hydrocarbon mixture such as naphtha ora naphtha fraction boiling inthe rangeabove about 175 F..containinguaboiitvolume per cent of aromatic hy-.

drocarbons, isdrawnirom `a source not shown Aand Hconducted .through a.pipe l' to the lower.. l

portion of a primary extractor 2. The extractor 1^ e advantageouslycomprises a vertical tower through which the feed hydrocarbon streamrises countercurrently to a downwardly moving body or stream of complexliquid.

The complex liquid is introduced to the upper portion of theextractorrthrough apipe 3 from a source which will' be referred tolater.

The complex is introduced to the extractor in the proportion of about 2to 4 volumes of complex per volume of feed hydrocarbon mixture. Theextraction in the extractor 2 is 'carried out at a temperature in therange of about (iO-120 F. and at a pressure which may be in the rangefrom atmospheric to 200 pounds per square inch sauge. u i

Provision may be made for continuously discharging used complex liquidfrom the system in an amount substantially equivalent to the amount offresh complex being formedy in situ.

As a result of the countercurrent contact occurring within the extractor2, extract and rafnatephases are formed. `The raflinate phase consistsessentially of paraffin and naphthene hydrocarbons and is continuouslydischarged from the top-of the extractor through a pipe 1.

The extract phase comprises complex and extract hydrocarbons, theextract hydrocarbons amounting'to from about 80 to 90 volume per cent ofaromatics, the remainder being non-'aromatics. This extract phase iscontinuously drawn olf from the bottom ofthe tower through a pipe Bvto asecondary extractor lil wherein it is subjected to the first stagewashing action.v

A wash solvent consisting essentially of saturated hydrocarbons boilingbelow 175 F; is conducted from a source not shown through a pipe l2 tothe lower portion of the extractor I0. The wash solvent is introduced inthe proportion of about 1 volume of solvent to 10 or 15 volumes ofprimary extract phase. The wash solvent rises through the towercountercurrently to the descending primary extract phase at atemperature in the range about 60 to 120 E'. and under a pressureranging from atmospheric to 200 pounds gauge.

Under these conditions the saturated extract hydrocarbons which arecoextensive in boiling range with the aromatic'extract hydrocarbons aredisplaced from the primaryextract phase in the form of asecondaryrailinate. This secondary raffinate is continuously discharged through apipe I3. y

The secondary extract phase accumulating in the bottom of the extractorI comprises complex, primary extract vhydrocarbons and some washsolvent. The wash solvent retained in the secondary extract phase willbe approximately equal in volume to the saturated hydrocarbons displacedtherefrom. It is continuously removed through a pipe I4 and conducted tothe upper portion of a tertiary extractor I5 which is advantageouslyoperated under conditions of temperature and pressure within the rangesdescribed for the secondary extractor I0.

Another stream of wash solvent liquid is conducted from the pipe I2through a branch pipe IS to the lower portion of the -extractor I 5 andis introduced thereto in the proportion of about 1 to 3 volumes ofsolvent per Volume of secondary extract phase.

4 mixture entering the extractor 2 through the pipe I.

As a result of the washing treatment in the extractor I5, substantiallyall of the aromatic constituents extracted by ther complex from the feedhydrocarbons in extractor 2 are displaced to form a tertiary rafnatewhich `is continuously discharged through a pipe i3 from the top of theextractor I5.

The stripped complex containing some wash solvent liquid ,iscontinuously discharged from the bottom of the extractor I5 through apipe I9 and is recycled all or in part through a branch pipe whichcommunicates with the previously mentioned pipe 3. That portionwhich isnot recycled and which may be regarded as used complex may be dischargedfrom the system at this point.

The volume of secondary extract phase flowing through the pipe I d issubstantially Vequal to the volume of primary extract phase flowingthrough the pipe 8 and will range from 2%" to 51/2 times the volume offeedhydrocarbon 7521s'v contemplated that the process may be ein.l

Referring again to the secondary extractor It), the secondary raffinateis conducted through the pipe l :tand may be recycled all or in partthrough a branch pipe 25 and pipe I to the primary extractor 2. In thisway the small amount of aromatic hydrocarbons that may be present inthesecondary rafnate are extracted therefrom upon further contact with thecomplex liquid. The.

recycled non-aromatic hydrocarbons are ultimately discharged asraffinate through the pipe 1.

On the other hand, provision may be made` for passing the secondaryraffinate allor in part to a fractionator unit 26 indicated in broken`lines for the purpose of separating the Washsolvent from the aromatichydrocarbons by fractional distillation. Thearomatic hydrocarbons may besegregated as a plurality of separate fractions as indicated. In' suchcase, provision may be made for recycling the separated aromaticfractions all or in part to the primary extractor 2.

The tertiaryl raflinateV discharged from the extractor I5 through thepipe I8 is likewise passed of the extracted hydrocarbons leaving theprimary i extractor 2 willbe about 82 to 87 volume per cent, while thearomatic content ofthe final extract hydrocarbons from the three stagesystem willY be about 91 to 97%. on the other hand, by omitting thesecondary extraction, the nal extract Y from the fractionation unit willhavethe same composition as that ofthe extract hydrocarbons from theprimary extraction. i

While mention has been made of using a wash solvent which is lowerboiling than the feed hydrocarbon mixture passing to the extractor 2,:nevertheless it is contemplated that the wash solvent'may be ahydrocar-bon or .hydrocarbon Amixture boiling in the lrange above thatof the The object is to use a wash feed hydrocarbons. solvent which isoutside the boiling range of the hydrocarbons which are to be displacedfrom the complexand Vwhich subsequently can be. separated readily lfromthe displacedl hydrocarbons by fractional distillation.

The feed rhydrocarbon mixture may be lany naphtha fraction containingbenzene'toluene and higher A.rr'iole'cular weight hydrocarbons, and itcaisses.

moved secondary extract phase through a teri,

tiary extraction zone in countercurrent Contact with another stream ofsaid Wash solvent liquid under substantially similar temperatureconditions and in the proportion of about from 1 to 3 volumes of solventper volume of secondary exl tract phase, removing from the tertiaryextraction zone a tertiary extract phase consisting essentially ofstripped complex, removing from the tertiary extraction zone a rainatephase consisting essentially of said Wash solvent and 1 aromatic primaryextract hydrocarbons, recycling said stripped complex at least in partto the primary .extraction zone, fractionating from the secondary andtertiary raiinate phases said wash solvent liquid and recycling therecovered wash 20 solvent liquid to the secondary and tertiaryextraction zones.

5. A process for extracting aromatic hydrocar bons from feed hydrocarbonmixtures of aromatic and non-aromatic hydrocarbons Which comprises 25bon complex of the Friedel-Crafts type, forming a primary extract phasecomprising` complex, aromatic and some non-aromatic hydrocarbons and aprimary raiiinateY phase consisting essentially of non-aromatichydrocarbons, discharging the primary raffinate phase, subjecting theprimary extract phase to countercurrent contact with a wash solventconsisting essentially of Y saturated hydrocarbons boiling below 175 F.in the proportion of about 1 volume of wash solvent per 10 to 15 volumesof primary extract phase, effecting said countercurrent contact at atemperature in the range about 60 to 126 F. such that non-aromaticextract hydrocarbons are displaced from the primary extract `phaseleaving a secondary extract phase comprising complex, aro.- maticprimary extract hydrocarbons and a small amount of Wash solvent,discharging the displaced hydrocarbons, subjecting the secondary extractphase to countercurrent washing with a further quantity of said washsolvent in the proportion of about from l to 3 volumes of said washsolvent per volume of secondary extract phase under substantiallysimilar conditions of temperature such as to displace said aromaticprimary extract hydrocarbons from the complex,

and removing the displaced aromatic extract hydrocarbons.

ERNEST A. NARAGON.

